1> Nothing is throttling. They may simply have enough other sources for the file to only need that much from you, or they're downloading a stupidly high number of torrent.
3> HELL NO. Adding a bunch of trackers only serves to increase the load on those trackers and doesn't actually help you.
4> Mostly yes, BUT, initial seeding in BitTorrent does NOT perform well in any tested scenario.
5> Ignore those they aren't relevant to your issue.
If you're GENUINELY the only one supplying data, make sure that the people downloading haven't been stupid in their settings. If they've followed those speedup guides from youtube, they are contributing MASSIVELY to the problems people have.